The present proposal offers a comprehensive approach to answer the questions posed by the Collaborative Clinical Trial Studying the Relationship between Glucose Control and Vascular Complications. The specific issues that this study will examine are the following: 1) the relative efficacy of intensively applied conventional therapy and insulin pump therapy in achieving improved metabolic control when compared with conventional therapy in Type I diabetes, 2) the feasibility of randomly applying these innovative therapies in Type I diabetics who have not been primarily selected for a high degree of compliance, 3) the acceptability of intensive conventional and pump therapies to diabetic subjects, 4) the effect of improved metabolic control and the different modes of therapy on the overall quality of life of the subjects, 5) the effect of the innovative therapies on prostaglandin metabolism and platelet function as well as on the standard metabolic indices of glucose and lipid metabolism, 6) the sensitivity and accuracy of new methods of measuring early diabetic retinopathy and neuropathy. In order to fully examine these issues, 15 Type I diabetics between the ages of 10 and 28 will be randomly assigned to a conventional treatment group, an "intensive" conventional group that will use home blood glucose monitoring and multiple insulin injections, or an insulin pump group that will utilize subcutaneous insulin therapy delivered with an external programmable pump. The inclusion of three, rather than two treatment groups will allow a comparison of the efficacy of two different innovative treatment modalities. It may also provide different degrees of control in the three treatment groups and allow an examination of a putative dose-response relationship between the degree of control and the development of complications. All three groups will be closely monitored with a variety of tests to determine metabolic status, compliance, acceptance of therapy, psychosocial impact of therapy, and any changes in retinal or neurologic disease. Many of the tests proposed are innovative and will be carefully evaluated to determine their utility for Phase III of the study.